1. Field of the Invention
This invention pertains to a power-generating system.
2. Description of the Related Art
Mobile power-generating systems or producers usually consist of a generator that is driven by an internal combustion engine. Commonly used as the generator are synchronous or asynchronous generators whose output voltage at the generator depends on the rotor RPM, i.e. on the engine RPM. If the engine RPM""s increase, the output voltage also increases, which in worst cases can lead to the destruction of the users connected to the power producer.
To this end, internal combustion engines of known power-generating systems have a mechanical control system that maintains the engine RPM at a predetermined value within its operating range. It is possible for the control action to be affected in such a way that the engine RPM can no longer be kept within the prescribed range, especially when the mechanical controller is disrupted, for example by control rods being blocked, broken springs, seized bearings or similar causes.
For expensive, technically complicated power generatorsxe2x80x94such as are known from DE 196 38 357 A1, for examplexe2x80x94another voltage control system is connected in series in addition to the RPM control system, and this additional voltage control system monitors the voltage produced by the generator and changes it by a suitable control means, such as through a rotor field control system or by changing the excitation. However, the voltage control system has no effect on the engine RPM. As a result, although the voltage can be held at a preset value, the generator voltage frequency continues to depend on the engine RPM.
DE 43 11 670 A1 describes a known circuit arrangement for a voltage controller located at a generator output with which the field current keying ratio can be detected at the generator. If the field current keying ratio is at a high level, i.e. if there is a large power draw by the users connected to the generator, this information can be detected directly by the circuit and processed, resulting in the RPM of an internal combustion engine that drives the generator being raised somewhat in order to satisfy the higher power draw at the generator.
From EP-A-0 352 759, a system to control actuating devices of an automobile is known having a safety concept characterized by the monitoring of equal elements of the individual functional chains as well as by the initiation of emergency measures if an error in one of the elements is detected during monitoring. The desired emergency measure is to either retain the current functional state or to change it in a direction that increases the safety level.
The objective of this invention is to provide a power-generating system that can prevent the above problems with respect to excess voltage increases at increased engine RPM and with respect to increased voltage frequency.
A power-generating system according to the invention an internal combustion engine, a generator driven by the internal combustion engine, a mechanical control unit to control a RPM of the internal combustion engine, a RPM-determining unit, and an electronic control unit coupled to the RPM-determining unit to control the RPM of the internal combustion engine, wherein the electronic control unit only controls the RPM, thus overriding an effect of the mechanical control unit, when the RPM-determining unit detects a RPM outside of a prescribed operating range.
According to the invention, an electronic RPM control system is superimposed or connected in series to the known mechanical engine RPM control system. If, due to a disruption of the mechanical controller, the engine RPM leaves the preset control range of the mechanical controller, in particular if it exceeds it, the electronic controller that was inactive up until then activates and influences the RPM of the enginexe2x80x94preferably by means of its ignition. Influencing the ignition can be done by interrupting it or by leaving out individual sparks. Also, the ignition timing can be changed.
Due to the effect of the electronic RPM control system connected in series, the RPM of the engine and thus of the generator stays within the prescribed RPM range. The output voltage at the generator also lies within the prescribed range accordingly with regard to its voltage level and frequency.
The electronic control system makes it possible to correct any erroneous behavior of the mechanical controller, which is an otherwise good way to control the engine with regard to its use and emissions.
It is especially advantageous if a display is provided to deliver an optical or acoustic signal, this display being activated when the electronic control unit is controlling the RPM.